KR20020034175A - Resol Based Binding Agent Containing Aluminium and Boron - Google Patents

Abstract

The present invention relates to a binder containing resol, base and water, further comprising at least one aluminum containing oxygen acid anion and at least one boron containing oxygen acid anion.

Description

Resol Based Binding Agent Containing Aluminum and Boron

The present invention relates in particular to resol based binder systems with improved ultimate strength.

EP-A 0 323 096 describes alkali resol resins which can be used for the production of cores and molds in the casting industry, where the resin is cured through the introduction of CO ₂ .

However, the strength of the cores produced in this way is lower than that of cores made by other gas curing methods (eg, polyurethane cold box method or epoxy SO ₂ method) even with increasing binder additives. Thus, the application of the so-called Resol CO ₂ method is limited to large single cores only.

On the other hand, despite the low strength, the castings are obtained in very good quality. Thus, to broaden the application of the Resol CO ₂ process, a binder that can be used to prepare higher strength moldings is desired.

The basic component of the binder described in EP-A 0 323 096 is an oxygen acid anion, in particular a boric acid ion. When the pH value of the resol decreases through the introduction of CO ₂ , the oxygen acid anion forms a stable complex with the phenolic resin, which causes the binder to cure.

As a substitute for borate salts, tartaric acid ions and aluminate ions are described in European Patent EP-A 0 323 096. Careful examination of the test data shows that the strength of the compositions containing tartrate or aluminate is clearly lower than that of the compositions containing borate. This is especially true for aluminates. Individual results using aluminates confirm this result.

There is a growing interest in broadening the range using the Resol CO ₂ method. Accordingly, it is an object of the present invention to provide a binder system that can be used in the Resol CO ₂ process and that can produce a higher strength core.

This object is completely achieved by a binder system comprising a resol resin, a base and water and further comprising at least one aluminum oxygen acid anion and at least one boron containing oxygen acid anion.

The present invention also includes a method of making a binder system of the present invention comprising preparing a resol resin and mixing the resol resin with a base, water and at least one aluminum oxygen acid anion and at least one boron containing oxygen acid anion. .

The present invention also includes aggregates and molding compounds containing a binder effective amount of the binder system of the present invention in an amount of up to 10% by weight based on the weight of the aggregates.

In addition, the present invention

1. mixing the binder system of the present invention with the aggregate in a binding amount of 10 wt% or less based on the weight of the aggregate,

2. pouring the molding composition obtained in step 1 into the mold,

3. curing the molding composition in the mold to obtain a self supporting form, and

4. Thereafter, the molding mixture formed in step 3 is removed from the mold, and further cured to produce a hardened, hard casting that is completely cured.

Another object of the present invention

1. To manufacture the casting core or mold of the present invention,

2. casting molten metal in or around the casting core or mold,

3. cool and harden the metal,

4. Subsequently, the method of casting a metal comprising separating the casting from the casting core or the mold.

A feature of the present invention is the combination of boron-containing oxygen acid anions and aluminum-containing oxygen acid anions, thereby improving the binder properties. Through these means, not only the extreme strength is positively affected, but the strength rises within the first two hours after the core is manufactured. Thus, cores made with the binder system of the present invention are more resistant to high moisture levels and aqueous coatings.

Resol resins are produced by condensation of a phenol component and an aldehyde component. Methods of making resol resins have been known for a long time and are described, for example, in A. Knop, W. Scheibe, Chemistry and Application of Phenolic Resins, Springer Verlag 91979 and European Patent EP-A 0 323 096. Preferred resol resins are described in European Patent EP-A 0 323 096. Preferred aldehyde resol resins consist mainly of molecules in which adjacent phenol groups are crosslinked via methylene bridges between the ortho and para positions, since these molecules have many complex sites for oxygen acid anions. Molecules in which phenol groups are combined through ortho-ortho-methylene crosslinking have very few complex sites for oxygen acid anions, so it is preferable that there are few such molecules or no such molecules are contained in the resol resin. For this purpose, all useful sites of the phenol group in the ortho position relative to the phenolic hydroxy group must be protected as methiolate.

As the phenolic binder, in addition to the most preferred phenol itself, a substituted phenol such as cresol or nonyl phenol or a phenolic binder such as bisphenol A is suitable and can be combined with phenol.

All aldehydes conventionally used in the preparation of resol resins can be used within the scope of the present invention. Examples of aldehydes are formaldehyde, butyraldehyde or glyoxal. Formaldehyde is particularly preferred.

Resol resins are preferably prepared by condensing phenolic components with aldehydes in the presence of a basic catalyst such as ammonium hydroxide or some alkali metal hydroxide. Preference is given to using alkali metal hydroxide catalysts.

The molar ratio of aldehyde (given formaldehyde) to phenol in the resol resin can vary from 1: 1 to 3: 1. However, the preferred range is 1.6: 1 to 2.5: 1.

Within the scope of the present invention, oxygen-containing anions are referred to as oxygen acid anions. It is a feature of the present invention that the binder system contains a boron-containing oxygen acid anion as well as an aluminum oxygen acid anion.

An example of the aluminum oxygen acid anion that can be used is aluminate, and borate can be used as the boron-containing oxygen acid anion.

Boron-containing oxygen acid anions and aluminum-containing oxygen acid anions can be used directly in their salt form. Salts mainly contain alkali or alkaline earth metals as cations, and sodium and potassium salts are particularly preferred due to their easy availability. However, it is likewise possible to produce oxygen acid anions in situ. Thus, aluminate is formed by dissolving an aluminum compound such as aluminum hydroxide or aluminum alcoholate in alkaline solution. Aluminum alcoholates are of the formula Al (OR) ₃ , wherein R may be a saturated or unsaturated, branched or unbranched hydrocarbon chain having 1 to 10 carbon atoms. Solutions of boron compounds such as boric acid or boric acid esters in alkaline solutions serve as solutions for boron-containing oxygen acid anions. Base solutions in water are preferred as alkaline solutions, likewise used for mixing with resol resins.

An Al: B atomic ratio of 0.05: 1 to 1: 1 of the boron containing oxygen acid anion and the aluminum containing oxygen acid anion is preferred for the purposes of the present invention. In this range, the cores are produced using the binder system of the present invention, the resulting cores exhibiting particularly good strength. A particularly preferred range is 0.1: 1 to 0.8: 1. The ratio of the sum of the boron and aluminum atoms in the boron-containing oxygen acid anion and the aluminum-containing oxygen acid anion to the number of phenol groups in the resol resin is 0.1: 1.0 to 1.0: 1.0, particularly preferably 0.3: 1.0 to 0.6: 1.0.

As the base, alkali hydroxides such as sodium hydroxide and potassium hydroxide are preferred. The molar ratio of hydroxide ions to phenol groups in the binder system is preferably from 0.5: 1 to 3.0: 1. In addition to the above components, the binder system of the present invention preferably contains water in an amount of 25 to 50% by weight relative to the weight of the compound. Water serves to dissolve the base and, if necessary, the oxygen acid anion. In addition, the binder should be imparted with a viscosity of 100 to 700 mPa · s that is suitable for application and ensures a uniform coating when mixed with the aggregates. Viscosity is measured using a capillary tube as described in EP-A 0 323 096.

The binder system of the present invention may also contain up to 25% by weight of conventional additives such as alcohols, glycols and silanes.

The binder system is prepared by mixing the resol resin with base, water and oxygen acid anions. It is possible to first mix the resol resin with an aqueous solution of base, and then to mix it as a solid or even in the form of an aqueous solution in an oxygen acid anion. It is also possible to first mix the oxygen acid anion with at least some base and at least some water and combine this mixture with the resol resin. Then, if necessary, the rest of the base and the rest of the water are added.

The binder system of the present invention can be used in combination with aggregates to produce molding compounds for use in the production of casting cores and molds. Casting cores and molds are used for example for the casting of metals. Aggregates and process steps used for this purpose are conventional and known from EP-A-0 183 782. To prepare the molding compound, the binder system is mixed with sand or similar aggregates. The molding compound contains the binder system of the present invention in a binding effective amount of 10% by weight or less based on the weight of the aggregate. Methods for obtaining a homogeneous mixture of binder system and aggregates are known to the skilled person. If desired, the mixture may also contain other conventional ingredients such as iron oxide, powder flax or wood fibers, pitch and mineral additives. In order to produce casting cores and molds from sand, the aggregates must be large enough in particle size. In this case, the core or mold will be sufficiently porous and volatile compounds may be removed during the casting process. The average particle size of the aggregates should generally be between 200 and 400 μm.

In the case of standard casting cores and molds, sand is preferred as the aggregate material, at least 70% by weight of the sand, preferably at least 80% by weight of silicon dioxide. Zircon, olivine and chromite sand are likewise suitable as aggregate materials.

Aggregate material is the main component of the casting core and the mold. In cores and molds of sand for standard applications, the binder portion is generally at most 10% by weight, often from 0.5 to 7% by weight, based on the weight of the aggregates. Particular preference is given to 0.6 to 5% by weight of binder relative to the weight of the aggregates used.

The casting is removed from the mold and then cured to maintain the outer shape. Conventional liquid or gas phase curing systems can be used for curing the binder systems of the present invention.

For example, the introduction of gaseous CO ₂ into the casting. However, low temperature curing with a liquid catalyst is equally possible. For example, there are methods of water free esters and resol esters which are well known as acetic acid esters and carbonate esters. After the casting is removed from the mold, the casting is further cured in a well known manner so that the casting is in its final state.

The invention is further illustrated by the following examples.

All quantities are by weight unless otherwise indicated.

1.Aluminum Resol Subsequent Addition of Al Compound to Standard Borate Containing Resol CO ₂ Binder

1.1 Preparation of Binder

With continued stirring, the standard borate-containing resol C0 ₂ binder (Novanol 140; boron: phenol molar ratio = 0.28: aluminum hydroxide or aluminum triisopropylate in the amounts shown in Table I as solids at a temperature of 40 to 50 ° C. 1, containing potassium hydroxide, was added to Ashland-Sudchemy-Kernfest GmbH. Stirring was continued until a uniform solution was produced.

Not Inventive Invention Binder number 1.1 1.2 1.3 1.4 1.5 Novanol 140 ^a 100 100 100 100 100 Aluminum hydroxide ^b - 2 - - - Aluminum triisopropylate ^c - - 2 3 4 Al: B - 0.4: 1 0.15: 1 0.23: 1 0.3: 1 ^a Ashland-Sutchemy-Kernfest Geembeha ^b Martinal ON, Martinswerk GmbH ^c Merck KgaA

1.2 Preparation and Testing of Molding Material / Binder Mixture

2.5 parts by weight of the binders listed in Table I were added to 100 parts by weight of Quarzsand H32 (Quarzwerke GmbH, Frechen) and mixed vigorously in a laboratory mixer. Using this mixture, specimens were prepared according to DIN 52 401 and then cured by gas treatment with CO ₂ (30 seconds, ₂ L CO ₂ per minute).

The strength of the specimen was measured according to the GF method. In this method, the flexural strength of the specimens was measured 30 seconds after preparation (immediate strength) and after 0.5 hour, after 1 hour, after 2 hours and after 24 hours. The core was placed in a wet chamber (98% relative humidity) and left for 24 hours to determine its resistance to high moisture levels. Thereafter, a test for moisture was performed. The strength of the specimens against the aqueous coating was measured as follows.

After 10 minutes of preparation, the cores were immersed for 3 seconds in the Miratec W3 aqueous coating (Ashland-Jutchemy-Kernfest GmbH). After 30 minutes at room temperature it was dried for 30 minutes at 150 ℃ in an air circulation oven. After the core was cooled, the flexural strength was tested.

The results are shown in Table II.

Not Inventive The present invention Binder number 1.1 1.2 1.3 1.4 1.5 Tensile Strength (N / cm ² ) Immediately 100 100 100 100 90 0.5 hour 120 160 150 160 140 1 hours 140 170 160 180 160 2 hours 150 180 180 190 170 24 hours 170 200 210 210 210 24 hours (98% relative humidity) 100 140 140 140 150 Aqueous coatings 110 180 150 150 140

As can be seen from Table II, the strength after only 2 hours of preparation using the binder of the present invention (numbers 1.2 to 1.5) is at least 24 hours after preparation using the unmodified binder (number 1.1) and at least Same. The strength when using modified binders then rose higher. Resistance to aqueous coatings and high degree of wetting was significantly improved by modifying with aluminum binder.

2. Aluminum resol obtained by dissolving aluminum compound in aqueous potassium hydroxide and adding this solution to phenol resin

2.1 Preparation of Binder

With the preparation of the commercial product, Novanol 140, after condensation of the resol resin, about 11.5 parts by weight of 50% potassium hydroxide was added to the product.

The amount of aluminum hydroxide shown in Table III was dissolved in 11.5 parts by weight of 50% potassium hydroxide. Novanol 140 was then prepared using this solution instead of pure potassium hydroxide to examine the effect of the manufacturing process on the properties of the binder system. The remaining constituents, such as borate and their quantification, were not changed.

To dissolve the aluminum hydroxide, potassium hydroxide was heated to about 95 ° C. with continued stirring and maintained at this temperature until a uniform solution was obtained. The aluminate solution was then added to the phenol resin at about 60 ° C. to avoid phase separation or crystal precipitation.

Not Inventive The present invention Binder number 1.1 ^a 2.1 2.2 2.3 Phenolic Resin Solution 88.5 88.5 88.5 88.5 50% KOH Solution 11.5 11.5 11.5 11.5 Aluminum hydroxide ^{b, c} - 1.0 2.0 3.0 Al: B - 0.2: 1 0.4: 1 0.6: 1 ^a Novanol 140, Ashland-Sutchemy-Kernfest Geembeha ^b Soluble in potassium hydroxide ^c Martinal Oen, Martinsberg Geembeha

2.2 Preparation and Testing of Molding Material / Binder Mixture

Preparation and testing of the molding material / binder mixture was the same as described in 1.2.

The results are shown in Table IV. A comparison of Tables II and IV showed that the aluminum binder showed the same benefits regardless of whether the aluminum compound was added to the binder in solid form or dissolved in aqueous potassium hydroxide.

Not Inventive The present invention Binder number 1.1 2.1 2.2 2.3 Flexural Strength (N / cm ² ) Immediately 100 110 110 90 0.5 hour 120 140 160 140 1 hours 140 160 160 150 2 hours 150 170 170 160 24 hours 170 200 210 200 24 hours (98% relative humidity) 100 120 150 140 Aqueous coatings 110 130 150 150

3. Comparative test: Aluminate completely replaces borate

3.1 Preparation of Binder

For comparison, two binders were prepared with the same composition as Novanol 140, except that borate was completely replaced by aluminate. Two similar resins were prepared by dissolving aluminum hydroxide in 50% potassium hydroxide as described in 2.1. The molar ratio of aluminate: phenol is shown in Table V.

Binder number 1.1 ^a 3.1 3.2 B: P 0.28 - - Al: P - 0.14 0.25 ^a Novanol 140, Ashland-Sutchemy-Kernfest Geembeha

3.2 Preparation and Testing of Molding Material / Binder Mixture

Preparation and testing of the molding material / binder mixture was carried out based on the method described in 1.2. The results are shown in Table VI.

Binder number 1.1 3.1 3.2 Flexural Strength (N / cm ² ) Immediately 90 ^-a 10 0.5 hour 120 - 20 1 hours 130 - 20 2 hours 150 - 20 24 hours 170 - 20 24 hours (98% relative humidity) 110 - 20 Aqueous coatings 110 - - ^a core cannot be manufactured

As can be seen from Table VI, exclusive use of only aluminate as the oxygen acid anion produces a core of very low strength at best.

Claims (13)

A binder system comprising (a) a resol resin, (b) a base, and (c) water, the binder system further comprising at least one aluminum oxyacid anion and at least one boron-containing oxygen acid anion. The binder system of claim 1 wherein the aluminum oxyacid anion is aluminate and / or the boron-containing oxyacid anion is borate. The binder system according to claim 1 or 2, wherein the aluminum oxygen acid anion is present as a solution of the aluminum compound in the alkaline solution and / or the boron containing oxygen acid anion is present as a solution of the boron compound in the alkaline solution. The binder system of claim 1 wherein the atomic ratio of aluminum to boron is from 0.05: 1 to 1: 1. The binder system according to any one of claims 1 to 4, wherein the ratio of the number of boron and aluminum atoms in the boron-containing oxygen acid anion and the aluminum-containing oxygen acid anion to the number of phenol groups in the resol resin is 0.1: 1.0 to 1.0: 1.0. . (1) preparing a resol resin, (2) A process for producing a binder system comprising mixing this resol resin with a base, water and at least one aluminum containing oxygen acid anion and at least one boron containing oxygen acid anion. The method of claim 6, wherein the resol resin is first mixed with an aqueous solution of base and then oxygen acid anions are added to the mixture. The process of claim 6, wherein the mixture is first mixed with a resol resin containing oxygen acid anions, at least some bases, and at least some water, followed by the remaining base if necessary and the remaining water if necessary. A molding compound containing the aggregate and the binder system according to any one of claims 1 to 5 in a binding effective amount of 10% by weight or less based on the weight of the aggregate. (1) the binder system according to any one of claims 1 to 6 is mixed with the aggregate in a binding amount of 10% by weight or less based on the weight of the aggregate, (2) the casting mixture obtained in step (1) is poured into a mold, (3) curing the casting mixture in the mold to obtain a self supporting form, (4) Subsequently, the molding casting mixture of step (3) is removed from the mold and further cured to obtain a hardened solid casting of a completely cured casting core and mold. The method of claim 10, wherein the casting mixture is treated with gaseous carbon dioxide to cure the casting mixture. The method of claim 10, wherein acetic ester or carbon dioxide ester is added to the casting mixture to cure the casting mixture. (1) casting a liquid metal in or around a casting die produced according to the method of any one of claims 10 to 12, (2) to cool and harden the metal, (3) then separating the cast object from the casting mold.